To enable to supply emergency electric power by using a power receiving terminal for emergency power supply without turning off a communication apparatus side even in the case of a single-phase two-wire system electric power.

First and second cables 60r, 60s are connected to a connecting terminal 74r for a first insertion leg of an input plug 70 connected to the power supply cable body 60, and a third cable 60n is connected to a connecting terminal 74s for a second insertion leg. A single-phase three-wire system output plug 80 and the first to the third cables are connected normally. Thus, since the third cable becomes a neutral wire, and between the first cable and the third cable, and between the second cable and the third cable, a voltage of 100 V with no phase difference can be obtained, single-phase two-wire system electric power can be supplied as a pseudo single-phase three-wire system electric power even when using a single-phase three-wire system power receiving terminal.